The present invention relates generally to coated substrates and methods of coating the same. In preferred embodiments, the present invention relates to transparent substrates having a hydrophobic (water repellant) coating thereon.
Glass is typically made of silicates that are melted to form a clear, transparent, solid material. The fundamental molecular structural unit of conventional glass is a SiO4 tetrahedron. Ordinary float glass (named for its production process whereby a molten ribbon of glass is floated on molten metal to provide a smooth surface) includes additional amounts of soda (Na2O), usually in the form of sodium carbonate or nitrate during the production process, lime (CaO) and other oxides (usually aluminum and magnesium oxides) to form a soda-lime-silica structure known colloquially as soda-lime glass. Other specialized glass can be prepared by the introduction of other additives and constituents.
It is sometimes highly desirable for conventional glass to have hydrophobic (water repellant) surface properties when employed in certain end-use applications, such as for automotive window glass. Various proposals exist to impart hydrophobic (water-repellant) properties to glass substrates. For example, U.S. Pat. Nos. 4,263,350, 4,274,856, 5,665,424 and 5,723,172 (the entire content of each being incorporated expressly hereinto by reference) disclose generally that glass surfaces can be coated with a vapor deposited layer of an chloroalkylsilane, such as dimethyldichlorosilane (DMDCS) so as to improve their hydrophobicity and/or release properties. Other proposals exist whereby a fluorinated alkylchlorosilane (FAS) coating may be employed to xe2x80x9ccapxe2x80x9d an underlayer on a glass substrate so as to improve coating durability. Please see in this regard, U.S. Pat. Nos. 5,328,768, 5,372,851, 5,380,585 and 5,580,605 (the entire content of each being incorporated expressly hereinto by reference). In addition, International Application WO 00/25938 (the entire content of which is expressly incorporated hereinto by reference) discloses that a silicon film consisting of chains of siloxane groups each terminating in an end molecule which reacts with water to form an OH group, may be capped by further reaction of that OH group with trimethylchlorosilane to form trimethylsiloxane chain ends.
While various hydrophobic coatings are known, there is still a need to provide such coatings with improved durability. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in substrates which exhibit improved hydrophobicity and durability. Most preferably, the substrate is glass. In some of the especially preferred embodiments of the present invention, coated substrates and methods are provided which include an SiOx-containing anchor layer comprised of a controllably humidified vapor phase deposition of a chlorosilyl group containing compound (most preferably silicon tetrachloride), and a hydrophobic capping layer chemically bonded to the SiOx-containing anchor layer.
In other especially preferred embodiments of the invention, highly durable hydrophobic coatings may be formed by the simultaneous aqueous vapor phase deposition of a chlorosilyl group containing compound and a chloroalkylsilane to form an anchor layer which may then be capped with a hydrophobic coating. For example, the simultaneous vapor deposition onto a glass substrate of silicon tetrachloride and dimethyldichlorosilane results in a hydrophobic coating comprised of polysiloxane chains crosslinked with silicon oxide branch points, derived from silicon tetrachloride (i.e. an insoluble reaction product), which may then be capped with a fluoro or chloroalkylsilane. Optionally, a silicon oxide (SiOx) layer may be vapor deposited prior to, and thereby disposed under, the cross-linked polysiloxane in the manner noted above.
In other embodiments of the invention, coated substrates on glass may be produced comprising a first anchor layer comprised of a controllably humidified vapor phase deposition of a hybrid organo-chlorosilane group containing compound, most preferably methyltrichlorosilane (MTCS). In other embodiments, various other combinations of hydrophobic and oleofillic capping layers may be chemically bonded to the hybrid layer.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.